Patrick picks former top aide from Stoughton as interim U.S. senator

Gov. Deval Patrick has announced that his former chief of staff, William “Mo” Cowan of Stoughton, will serve as interim U.S. senator. Cowan will fill the seat vacated by newly confirmed Secretary of State John Kerry until a special election is held in June.

Gov. Deval Patrick announced Wednesday morning that his former chief of staff, William “Mo” Cowan of Stoughton, will temporarily fill the U.S. senate seat left vacant by John Kerry’s confirmation as U.S. Secretary of State.

Cowan, 43, is a North Carolina native and Duke University graduate. He was Patrick’s chief of staff for 11 months, and is considered one of the governor's confidants and close advisers. He left the job earlier this month, saying he wanted to take a job in the private sector and be with his family.

When Patrick introduced him at the State House, Cowan said he's "honored and humbled" by the appointment. He said he'll work "as hard as humanly possible" for the needs and hopes of the state's residents.

Patrick said the state will benefit from Cowan's wisdom and judgment while he's in the U.S. Senate. State Senate President Therese Murray, D-Plymouth, also praised Cowan as a "consummate professional" with a spotless reputation.

She said he would have been a great special-election candidate, had he chosen to run for Kerry's seat.

Cowan joined Patrick's administration in 2009 as the governor's legal counsel, and before that was a partner with Boston’s politically connected Mintz Levin law firm.

Kerry was confirmed as President Barack Obama’s secretary of state Tuesday. A special election to fill the vacancy will be held June 25.